Undesirable airborne compounds, including chlorine and sulfur containing compounds, ammonia, formaldehyde, urea, carbon monoxide, oxides of nitrogen, mercaptans, amines, and ethylene, occur in a number of environments, where most primarily are responsible for the presence of disagreeable odors, irritating or toxic gases. Such environments include petroleum storage areas, refineries, water treatment facilities, sewage treatment facilities, hospital morgues, animal rooms, swimming pools, and pulp and paper production sites, among others.
Facilities storing hazardous quantities of chlorine or sulfur dioxide must invest in emergency standby equipment to prevent accidental chemical releases. The Environmental Protection Agency's (EPA's) Risk Management Program for Chemical Accident Release Prevention “requires regulated facilities to develop and implement appropriate risk management programs to minimize the frequency and severity of chemical plant accidents.” in addition, “a performance-based approach towards compliance with the risk management program rule is required.”
The Uniform Fire Code, Article 80, states that the full contents of the single largest storage container of chlorine must be mitigated in 30 minutes. If a toxic gas release were to occur from a 1-ton cylinder of chlorine, the laws of thermodynamics suggest that approximately 400 lbs of liquid chlorine would flash into vapor and the remaining contents of the chlorine cylinder would spill out as a liquid at its boiling point. According to American Water Works Association (AWWA) Risk Management Program Guidance, the outer limit of the impact area in a chlorine release, is drawn at a five-mile radius in all directions from the point of impact.
Chlorine (Cl2) is a greenish-yellow dense gas with a suffocating odor. The compound is used for bleaching fabrics, purifying water, treating iron, and other uses. Control of this powerful irritant is most desirable for the well-being of those who work with it or are otherwise exposed to it. At lower levels, in combination with moisture, chlorine has a corrosive effect on electronic circuitry, stainless steel and the like. Accordingly, protecting electronic apparatus from the corrosive fumes of chlorine and chlorine by-products is desirable.
Sulfur dioxide (SO2) is a colourless gas. It can be oxidized to sulfur trioxide, which in the presence of water vapour is readily transformed to sulphuric acid mist. Health effects caused by exposure to high levels of SO2 include breathing problems, respiratory illness, changes in lung defences, worsening respiratory and cardiovascular disease. People with asthma, chronic lung or heart disease are the most sensitive. SO2 also damages trees and crops. SO2, along with nitrogen oxides, are the main precursors of acid rain. This contributes to the acidification of lakes and streams, accelerated corrosion of buildings and reduced visibility.
Hydrogen sulfide (H2S), a colorless, toxic gas with a characteristic odor of rotten eggs, is produced in coal pits, gas wells, sulfur springs, and from decaying organic matter containing sulfur. Controlling emissions of this gas, particularly from municipal sewage treatment plants, has long been considered desirable. More recently, protecting electronic apparatus from the corrosive fumes of these compounds has become increasingly important. H2S is also flammable.
Ammonia (NH3), also a colorless gas, possesses a distinctive, pungent odor and is a corrosive, alkaline gas. The gas is produced in animal rooms and nurseries and its control also has long been considered desirable.
Formaldehyde (HCHO) is a colorless gas with a pungent suffocating odor. It is present in hospital morgues, and because it is intensely irritating to mucous membranes, its control is desirable.
Urea (CH4N2O) is present in toilet exhaust and is used extensively in the paper industry to soften cellulose. Its odor makes control of this compound desirable.
Carbon monoxide (CO), an odorless, colorless, toxic gas, is present in compressed breathing air. Oxygenation requirements for certain atmospheres, including those inhabited by humans, mandate its control.
Oxides of nitrogen, including nitrogen dioxide (NO2) nitric oxide (NO), and nitrous oxide (N2O), are compounds with differing characteristics and levels of danger to humans, with nitrous oxide being the least irritating oxide. Nitrogen dioxide, however, is a deadly poison. Control of pollution resulting from any of these oxides is desirable or necessary, depending on the oxide.
Mercaptans and amines, including methyl mercaptan (CH3SH), butyl mercaptan (C4H9SH) and methyl amine (CH5N), are undesirable gases present in sewerage odor. The control of these gases is desired for odor control.
Ethylene (C2H4) is a colorless, flammable gas that is a simple asphyxiant which accelerates the maturation or decomposition of fruits, vegetables, and flowers. Control of this compound prolongs the marketable life of such items.
Attempts have been made to provide a solid filtration media for removing the undesirable compounds described above. Desired features of such media are a high total adsorption capacity for the targeted compound, high efficiency in removing the compound from an air or gas stream, and a low ignition temperature (non-flammability). For example, U.S. Pat. No. 3,049,399 describes a solid oxidizing system in pellet form composed of activated alumina, Al2O3, impregnated with potassium permanganate, KMnO4. This pellet provides air purification and odor control by both adsorbing and adsorbing odors, and then destroying the collected odors by the potassium permanganate's controlled oxidizing action.
Activated carbon will physically adsorb considerable quantities of hydrogen sulfide. See, for example, U.S. Pat. No. 2,967,587. See also French Patent No. 1,443,080, which describes adsorption of hydrogen sulfide directly by activated carbon, which is then regenerated by hot inert gas or superheated steam.
Better removal of sulfur compounds can be accomplished by the catalysis of the oxidation of hydrogen sulfide to sulfur, based on the ability of carbon to oxidize hydrogen sulfide to elemental sulfur in the presence of oxygen. Ammonia may be added to an influent gas stream of hydrogen sulfide and oxygen to provide catalysis. Silicate-impregnated activated carbon is also effective. The residual adsorbate, however, may not be removed by extraction with alkaline solutions. See South African Patent No. 70/4611. Treatment with a 1% solution of NaOH restores the adsorption capacity of activated carbons used for adsorption removal of hydrogen sulfide gas. Boki, Shikoku Igaku Zasshi, 30(c), 121-8 (1974) (Chemical Abstracts, Vol. 81).
See also, for example, French Patent No. 1,388,453, which describes activated carbon granules impregnated with 1% iodine (I2) for this use. South African Patent No. 70/4611 discloses the use of silicate-impregnated activated carbon. Swinarski et al, Chem. Stosowana, Ser. A 9(3), 287-94(1965), (Chemical Abstracts, Vol. 64, 1379c), describe the use of activated carbon treated with potassium salts, including potassium hydroxide (KOH) for hydrogen sulfide adsorption. Activated carbon has also been impregnated with a solution of sodium hydroxide (NaOH) and potassium iodide (KI).
In U.S. Pat. No. 3,391,988, mercaptans are removed from exhaust gas by contact with an adsorbent impregnated with a liquid mixture of an alkaline material. Subsequent patents have taught different treatments of activated carbon with NaOH and, optionally, lead acetate (PbOAc), and have indicated the influence of the chemical reaction therein combined with the physical adsorption of the activated carbon. See U.S. Pat. No. 4,072,479 and U.S. Pat. No. 4,072,480. Although not confirmed, U.S. Pat. No. 4,072,479 suggests that hydrogen sulfide is oxidized to elemental sulfur in the presence of activated carbon, and that the presence of moisture on the activated carbon is significant. Another method for removing sulfur and other compounds from gas streams utilizes a product known as Purakol K (Lindair, Ljusne, Sweden). This product contains carbon impregnated with NaOH and KI.
Other uses of impregnated carbon include removing water from air (desiccation), see, for example, Soviet Union Patent No. 1,219,122 (activated carbon combined with aluminum oxide; a binder, calcium hydroxide; and lithium bromide); and the removal of acidic contaminants from gas streams, see, for example, U.S. Pat. No. 4,215,096 (activated carbon impregnated with sodium hydroxide and moisture, for the removal of chlorine from gas streams) and U.S. Pat. No. 4,273,751 (activated carbon impregnated with sodium hydroxide and moisture, for the removal of sulfur oxide gases and vapors from gas streams).
Japanese Patent No. 61-178809 teaches water purification by treatment with activated carbon loaded with metallic copper or copper salts. Several patents teach alumina and carbon adsorbents, including U.S. Pat. No. 3,360,134 (alumina hydrate contacted with a carbonaceous solution; used as a decolorizing agent, a reviving agent for precious metal electroplating bath for the removal of constituents from cigarette smoke, and as an adsorbent in pressure or gravity flow percolation beds); U.S. Pat. No. 4,449,208 (powdered carbon, dense alumina, and a binder, for increasing heat capacity of the adsorbent to enhance the operation of adiabatic pressure swing adsorption processes by decreasing the cyclic temperature change in the adsorbent bed during each cycle of the process); U.S. Pat. No. 3,819,532 (ground graphite and finely divided alumina adsorbent, for removing aromatics, heterocyclics, sulfur compounds, and colored materials from lubricating oils); and U.S. Pat. No. 3,842,014 (ground graphite and alumina binder, for adsorbing paraffin). Such art generally teaches a substrate consisting primarily of activated carbon with a relatively small amount of alumina.
None of the compositions described to date have effectively solved problems surrounding the combustibility of activated carbon. This problem can be critical in installations such as nuclear power plants.
Furthermore, none of the methods available thus far have effectively addressed neutralization of large quantities of gases. Accordingly, there remains a need in the art for a composition having an enhanced capacity for chlorine and sulfur dioxide removal. Furthermore, there remains a need in the art for a composition that can operate at low atmospheric temperatures.